WSU archaeologist focuses research on ancient social change

Wednesday, March 06, 2013

By Lainie Rusco

After only one year, assistant anthropology professor Lisa Overholtzer is making a name for herself at Wichita State University.

Overholtzer, who joined the WSU faculty in 2012 after holding adjunct instructor positions at Northwestern University and DePaul University, has been in the scientific news recently for her research in central Mexico.

Together with experts from the University of Texas at Austin and Washington State University, Overholtzer is researching whether the Aztecs who conquered the city of Xaltocan in ancient Mexico around the year 1435 changed the genetic makeup of those who lived there.

The study – called the Xaltocan Archaeological Project – was published in the December issue of the American Journal of Physical Anthropology.

UT Austin graduate student Jaime Mata-Miguez is first author on the paper. Other collaborators include Deborah Bolnick (director of the DNA lab at UT Austin); Enrique Rodriguez-Alegria (archaeologist at UT Austin); and Brian Kemp (DNA expert at Washington State).

“I was interested in how the lives of ordinary people changed when they were conquered and then incorporated into the Aztec empire,” Overholtzer said.

Significant research

Colonial documents recount that when the site was conquered, all of its original Otomi inhabitants fled, leaving the site empty for 40 years until the Aztec king sent taxpayers to repopulate the island.

Overholtzer’s archaeological excavations, though, suggest that there was continuity in occupants.

“Houses were built, and burials were interred in the exact same spot in the houses I excavated, and radiocarbon dates showed that there was no 40-year abandonment period,” she said.

Overholtzer thought some of the answers might lie at the molecular level in the DNA of the family members buried underneath the house patios.

To further investigate that question, she collaborated with ancient DNA experts at the University of Texas at Austin. So far, they have conducted mitochondrial DNA sequencing, which shows there was indeed some form of demographic shift in at least some households.

The reason for that shift is unclear, Overholtzer said. One theory is that there might have been some demographic change, but not a complete replacement of the population.

Overholtzer points out that her study is preliminary and that ancient DNA analyses are ongoing.

The research is significant, though, because it is the first to examine the genetic impact of Aztec imperialism and is using molecular anthropology techniques to address new questions of social dynamics and demographic shift in the region.